Conventionally, there are technologies for determining subject's arousal level with no burden on a subject by using subject's biological information. For example, there is a conventional technology to track changes in a feature point at which spectral density calculated from subject's heartbeat signals by frequency analysis reaches its local maximum, thereby determining subject's arousal level. For example, by applying this conventional technology to a vehicle, driver's arousal level can be determined, and it is possible to inform the driver of a risk.
To determine subject's arousal level by using this conventional technology, it is necessary to acquire a feature point stably.
Patent Literature 1: Japanese Laid-open Patent Publication No. 2010-155072
Patent Literature 2: International Publication Pamphlet No. WO 2008/065724
However, there is a problem that if a feature point calculated from heartbeat signals by frequency analysis is indistinct, it may fail to determine subject's arousal level.